Does Lest Have The Same Meaning As Unless?

No, it doesn't. "Lest" is an old word, almost out of use now. You only really find it in poetic expressions like "Lest we forget" (often used in connection with the soldiers who died in World War I, though the phrase actually comes from an older poem by Rudyard Kipling.) The nearest equivalents in modern English would be "in case" or "for fear that" and it is always followed by a subject and a verb. An example sentence might be:

I daren't touch the china vase, lest I break it. (ie., I am so afraid of breaking it that I won't touch it.

"Unless" has the same position in a sentence, but means "if not." Example sentences could be:

I'll go for a picnic tomorrow unless it rains (ie., if it doesn't rain)

I won't go unless you do (ie., if you don't go.)

Think About It....
Here Are Some Sscentences You might Be Able To See The Difference
"Less We Forget" ANZAC Slogon
"Unless We Do Something"
"Less Of The Capacity" Talking Mathematicion Language.
Description Me More Please So I May Edit And Re Operate My Answer.

I think of it meaning something like "if" but with a warning. It wouldn't be good if whatever it is happens.

Nope.....anything